Officially, the world's fastest jet-powered aircraft remains the SR-71
Blackbird. Although the official record is about Mach 3.3 (or 3.3 times the speed of sound), many believe the
aircraft could actually fly much faster. However, it seems unlikely that the SR-71 could go much faster than about
Mach 3.5, with a very slim chance of Mach 4, due to propulsion and structural limitations. By Mach 3.6 or 3.8,
shock waves generated by the nose of the aircraft are formed at an angle such that they impact the engine nacelles
and cause the engines to unstart. In addition, heat generated by the aircraft's high speed increases to the point
that certain portions of the plane's structure begin to fail by about Mach 3.5.

Since this article was originally published, the SR-71's speed record has been broken by NASA's
X-43 Hyper-X experimental aircraft. This unmanned
vehicle was designed to test an experimental engine called a scramjet at speeds ranging from Mach 7 to Mach 10.
At the X-43's cruising altitude of 100,000 ft(30,510 m), these Mach numbers correspond
to speeds of approximately 4,750 mph(7,640 km/h) to 6,750 mph(10,855 km/h).

The scramjet, which stands for supersonic combustion ramjet, is a subclass of the
jet engine. However, the X-43 was accelerated to these high Mach numbers
by a booster rocket, and the aircraft only flew under scramjet power for a few seconds before falling into the
sea. From a purist's point of view, the X-43 did not truly break the jet-powered aircraft speed record since it
was incapable of cruising at and sustaining these high speeds.

Nonetheless, some believe the SR-71's speed record has already been bested by its supposed replacement dubbed the
Aurora. If this mysterious new spy plane does indeed exist, it is
believed to cruise at speeds ranging from Mach 5 to Mach 8 at 100,000 ft(30,510 m).
These Mach numbers correspond to speeds of 3,380 mph(5,435 km/h) to
5,400 mph(8,685 km/h). The Aurora may use scramjets, pulse-detonation wave engines, or
some other exotic form of propulsion to reach these speeds. However, we should stress that there is no conclusive
evidence that this plane ever existed.

As of the writing of this answer, the official speed records for the fastest flying animals and machines are
listed below.

Note that the insect record is still the subject of much debate since it is difficult to reliably measure the speed
of a flying insect with repeatability. The dragonfly speed has been measured fairly consistently, though some
sources indicate even higher speeds of up to 43 mph (70 km/h) have been recorded. Smaller species of insects are
more difficult to measure as demonstrated by an entomologist who claimed to have clocked a deer botfly at 800 mph
(1,290 km/h), faster than the speed of sound! Though this record has since
been debunked due to poor experimental practices, more recent investigators have measured the tabanid fly at 90 mph
(145 km/h).

Speed records for birds are also subject to controversy as different sources claim the fastest is the swift, the
pergrine falcon, or the frigate bird. Again, the red-breasted merganser (a species of duck) seems to be the most
consistent and repeatable record. However, one researcher claims to have measured a spine-tailed swift at 106 mph
(170 km/h). The true record-holder often depends on how the speed was measured and the exact wording of the
record.
- answer by Doug Jackson, 22 April 2001